Stormageddon

In the first week of June, four states were battered by a ferocious east coast low unusual in its size, damaging storm surge and intense rainfalls. Tasmania was under a deluge as an unprecedented seven rivers broke their banks in torrential downpours. Huge seas and an unusual wave direction carved out huge sections of waterfront properties and flooded low lying areas. Did warmer temperatures play a role? How are storm patterns changing across Australia and will we see more like this?

TRANSCRIPT

NARRATIONA ferocious weather event that tore down Australia's east coast in the first week of winter. In just a few days, it wreaked havoc from Queensland to Tasmania. Waterfront foundations were swept away. Extreme flooding caused deaths, widespread road closures and evacuations. As the clouds cleared, the debate began on whether Stormageddon was truly a weather system out of the ordinary or part of a new trend.

Assoc Prof Lisa AlexanderCertainly in the last 50 years, we haven't really seen any trends.

Assoc Prof Ian GoodwinThat's the sort of thing we're gonna see in the future.

Prof Ashish SharmaThe subtle shift makes the storms more intense.

Anja TaylorHow are storms changing across Australia and is this a taste of our climate change future?

NARRATIONThere's nothing unusual about an east coast low, the type of storm system that usually batters eastern Australia between late autumn and winter. But right off the bat, forecasters at the Bureau knew this one was going to be big.

Dr Karl BraganzaSo the system started on 3 June, quite typically, just off the coast of south-east Queensland, but after that it started to become unusual, so it interacted with quite a deep trough extending from New Caledonia up in the north-east, right through the Tasman, into southern New South Wales. In terms of the spatial footprint of this system, it was very unusual.

NARRATIONAn intense stationary high-pressure system over New Zealand was blocking the east coast low from spinning out to sea and driving it south.

Dr Karl BraganzaNormally we tend to have one or two parts of the coast really copping the brunt of the storm, but for this one it really tracked all the way down, so we had flooding across catchments right down New South Wales, Victoria and Tasmania.

NARRATIONBy Sunday, Tasmania was under water.

LukeAnd I moved the dairy cows to here on some of the higher ground and there was 320 stranded. And then the water just exploded, it just come from nowhere. And when I came back at three o'clock in the morning, they were all gone. They were all washed away.

Dr Karl BraganzaWhat we saw was record rainfall over three days, and, you know, something like five rivers in flood at the same time in northern Tasmania, and that's quite unprecedented. And, really, the sheer volume of water was really reflective of just how much water was in the atmosphere.

NARRATIONHeavier rainfalls normally occur in warmer months because a warmer atmosphere can carry more moisture. In this case, it wasn't just the atmosphere but the seas were also abnormally warm.

Dr Karl BraganzaTo May, the Tasman Sea was almost double its previous record, so we had really, really very high sea surface temperatures in the Tasman. You saw this system basically sitting off the coast directing the airstream over that warm water into Tasmania.

Anja TaylorWould you say that the warmer weather definitely played a part in how much rainfall Tasmania got?

Dr Karl BraganzaThose sorts of attribution studies take some time. But certainly just based on basic understanding of meteorology, then the things line up quite closely.

NARRATIONSo this was definitely an unusual storm in its size, with warmer than normal weather conditions likely contributing to the extraordinary rainfall. But surprisingly, these east coast lows are predicted to decrease, not increase in frequency, as the climate warms.

Dr Karl BraganzaAnd that's largely because the atmosphere becomes a bit more stable under climate change, so both the tropical cyclones and east coast lows, there's an overall likely reduction in number, but the proportion of these heavier storms tends to increase and that's because when the meteorology is right, we've just got that much more energy for the storm from the sea surface temperatures underneath.

NARRATIONA team at the University of New South Wales have also found tropical expansion from climate change is likely to push more east coast lows off the mainland.

Assoc Prof Lisa AlexanderWe're likely to see a shift of the storm tracks to the south. And that just means that, you know, we're still gonna get storms, they just won't hit...they'll hit further south than they currently do. So that's why we might see a decrease in the frequency of them. A decrease in frequency doesn't mean a decrease in damaging events because what we're seeing is climate change will also bring rising sea levels and bigger waves.

NARRATIONBig waves and high seas were a major damaging force in this recent storm and they took particular aim at the southern end of beaches. Some of the most spectacular damage was seen here at Collaroy in New South Wales.

Prof Ian TurnerThis is the largest erosion event that I've seen in my career working on the Australian coastline. We saw the beach narrow by as much as 50m, we saw a swimming pool on the beach. A lot of sand was moved.

Anja TaylorI'm standing here on a rock wall that was built to protect the property behind me. Usually you can't see any of these rocks because the sand completely covers them.

NARRATIONIn total, around 40m width and several metres depth of sand disappeared from the beach. But apparently it all comes back. For the last 40 years, a team from the University of New South Wales have been using a variety of imaging equipment to map this shoreline.

Prof Ian TurnerWe use conventional survey equipment, we have cameras mounted on rooftops, we fly aeroplanes with a laser scanner and we fly drones. What we're trying to understand is how the sand is moved by the ever-changing wave and water level conditions. Over the 40-year monitoring program here at Narrabeen-Collaroy, there's actually been no sand lost.

NARRATIONAlthough the beach has shifted in shape, the overall volume hasn't changed.

Prof Ian TurnerSand is stripped from the dunes and deposited out at the sand bars, but it always comes back.

NARRATIONIt's small comfort to those that just sustained severe property damage from such a big erosion event.

Anja TaylorSo what has made this storm, in particular, so diabolical?

Prof Ian TurnerWell, there are three things that have come together over the weekend. First of all, we had large waves. So, waves were recorded offshore Sydney on Saturday night up to 13m. But by coincidence, those large waves coincided with king tides, so over 2m tides, so that brought the water level high. And then the third thing, which is perhaps most unusual, is the storm direction. The storm came from the east-north-east and that's relatively unusual for our stretch of coastline and it exposed areas like this, that generally are a bit more protected, it exposed them to that wave energy.

Anja TaylorSo why is it coming from that direction?

Prof Ian TurnerOh, look, it's just how the east coast low storm developed. It's a natural process. It does happen. That one happened to come from the north-east.

NARRATIONWhile the king tides were nothing to do with warmer weather, they do give a good picture of what future sea level rise might look like, and the other two factors of this mighty storm surge - big waves and a north-east swell - might be a shift we can expect more often. It couldn't look less like Stormageddon at Hawks Nest in New South Wales, but it's here I'm starting to understand why the north-east shift had such a powerful effect.

Assoc Prof Ian GoodwinThis black nor'-easter generated waves 1,500km away, almost into the Coral Sea. These long wavelength waves, as they moved across the continental shelf, were shoaling to produce very high wave heights. 15 to 25-foot faces were surfed during this period and produced the storm erosion along the coastline.

Anja TaylorSo why do they call it a black nor'-easter?

Assoc Prof Ian GoodwinThe black nor'-easter refers to when the skies go black, dark grey, the winds are gale force. We don't think of high-pressure systems as capable of producing storm waves, but when those high-pressure systems become really intense, the winds often produce these large waves and when combined with an east coast low, they produce the most extreme storm wave environment.

NARRATIONNormally we think of a high-pressure system as bringing calm and lovely weather like today, but the intense high over New Zealand not only squeezed Stormageddon into the coast, it fuelled it with the intense, warm, moist winds that brought such dramatic rainfall.Ian Goodwin is a paleoclimatologist and as he digs into our stormy past, he's convinced we'll see more and more of these big blocking highs and black nor'-easters.

Assoc Prof Ian GoodwinWhen most of us go down to the beach, we see sand. But for us, we look at the sand much like someone studying tree rings or if we're studying the layers in an ice core - that each successive period of coastal deposition or erosion is actually recorded within our undeveloped coastline. We use aerial LiDAR to produce fine resolution digital elevation models and then we use ground penetrating radar to look into the sand deposition. We then need to know when each of these periods occurred. When a sand grain is deposited by waves on a beach, and then buried by the next wave, its clock, or how long it's been buried, starts at that point. And the quartz grains in that sand and the feldspars attract radiation from the surrounding heavy mineral sands. We then come along and we want to extract a sample in total darkness, bring it back to the laboratory and then measure how much radiation is in that quartz grain and hence use it as a clock.

NARRATIONIt's like developing an ancient sand grain photograph in the dark room. Depending on how successive layers at the beach were deposited and when, it reveals the dominant wave and wind patterns throughout history.

Assoc Prof Ian GoodwinOne of the things I got excited about when I saw that storm developing was that was the type of system that we had reconstructed as being much more frequent during the period from about 1650 AD to 1800 AD.

NARRATIONDuring each stormy period when the black nor'-easter was more frequent, it was also a period of tropical expansion and that's what's happening in today's climate.

Assoc Prof Ian GoodwinIt's quite a straightforward understanding that as the tropics expand the subtropical air masses are influencing more of the east Australian coastline and that combined with low pressure systems coming out of the Southern Ocean produces more of these storms that approach our coastline from the east through to the north-east.

NARRATIONIf Ian's predictions are right, the explosive wave, wind and rain combination of Stormageddon will become a more regular feature of our climate change future. It may leave the southern ends of beaches particularly vulnerable to property damage. While storm surge affects those close to the beaches, it's flooding from torrential rains that can grind whole cities to a halt.

Prof Ashish SharmaIn an urban flooding environment, you can't go for shopping, go to work. Your day to day civil life that you take for granted is put on hold, and this has a massive disruption on the way society functions.

NARRATIONLike many other streets, Botany Road looked very different under heavy rainfall last month. The rain simply came down too fast.

ManHere we go. Help's on the way.

Prof Ashish SharmaThe reason any urban area floods, it's not because of the amount of rain that comes down by itself but it's the rate of the rainfall. If the rate is really high, the urban area, the stormwater infrastructure that is in place, cannot cope because the water has no other place to run off to.

NARRATIONAt the University of New South Wales, Professor Sharma and Conrad Wasko have been looking at how rainfall patterns have changed over more than 40 years.

Prof Ashish SharmaWe looked at a collection of storms, something close to 40,000 storms across Australia, all climate zones in Australia, and we found consistently the storms were getting more intense, more concentrated in time and in space. And this is what is so impactful, this is why the study has been noticed so much across the world.

Prof Ashish SharmaIf the storm were three-minute bursts of rain, that part is massive. This big flood cannot anymore be contained by the infrastructure that was designed many years ago to withstand a flood that would be spread over a longer period of time. And we found 100% result - all the locations that we looked at were finding exactly the same pattern - that the storms were intensifying with warming climates.

Anja TaylorThe research here at the University of New South Wales is the first to show that flooding from storms will increase in cities due to climate change.

NARRATIONWe can never blame any single storm on climate change, and the so-called Stormageddon is no exception. But it's an interesting example because its influences include warmer, high seas and a warmer atmosphere - all predicted to intensify the effects of storms in the future.So what, if anything, can we do to prepare? When it comes to floods, hanging on to our green spaces within urban environments is vital to cope with more intense bursts of rain.

Prof Ashish SharmaIf you have that storm fall on concrete, it will come out as a very intense flood. If this storm falls on to a landscape that can absorb the impact of the storm, it will dampen the flood peak. That just stretches the flood out to a longer time span. If the flood gets stretched, then that intense peak that you are having, that can stop.

NARRATIONWith greater storm surge due to sea level rise, we may need more mitigation strategies like beach replenishment. But ironically, bigger storms from the north-east may help with that.

Assoc Prof Ian GoodwinStorms are seen as evil. They're the bad guys because we see what they produce in terms of storm erosion and we look at houses falling into the ocean and so on. But, in fact, whilst they are causing that erosion, the higher wave energy out in the deeper water is actually mobilising sand on the seabed and helping to transport that towards our coast. So a decline in storm activity means less sand transported to our coast and hence our coastlines would recede faster with sea level rise. So we need to wish for more storms.

YOUR COMMENTS

Why has it taken eight years for the scientists at our universities to catch up with what is unfolding?

How long will it take them to focus on the other issue to affect the Sydney basin or should we wait for the shakes to unfold and then watch with wonder the analysis being done after the events.

Simon - 22 Jul 2016 2:08:03pm

I would like to have seen an bigger exploration of professor Ian Goodwill's history of storm and climate over the last 1000 years. You briefly touched on the similarities of climate 300 years ago, with the phenomena of tropical expansion, but that was it. I would have thought that this required further questioning. Especially a discussion of what followed that particular 50 year period.

roslynl - 25 Jul 2016 9:25:49am

We agree that Prof Goodwin's research easily warrants more air time for a more indepth exploration, however as is often the case in a half hour program, we are limited by the time we have to cover all the relevant research. Below is a link to Prof Goodwin's recent paper which provides more detail.

http://onlinelibrary.wiley.com/doi/10.1002/2016JC011769/full

Bill - 20 Jul 2016 7:36:46pm

Hi Anja,

Thanks for an interesting story about the recent Stormageddon.

Do you think it's a taste of much bigger storms to come?

While watching the imagery of the rough seas in the story, I remembered a poster that was hanging on the wall of a medical centre in Box Hill. The picture was of a really stormy sea & a dark sky, with some rays of sunlight piercing the grey clouds. The caption at the bottom of the poster was..."Anyone can steer the ship when the sea is calm".

I'm a bit curious about all that sand that got washed away from Collaroy beach & how long it might take to wash back in. When you were having a friendly chat (off camera) with Prof Ian Turner & Prof Ian Goodwin, did they happen to guesstimate how long it might take for the displaced volume of sand to return naturally to Collaroy beach?

Down at Portsea on the Mornington Peninsula, the bayside beach landscape & tide flow has really changed since the channel was deepened at Port Phillip Heads. Although heavy duty sandbags were installed at the back of the beach some years ago to slow the erosion, the sand doesn't look like it will be returning naturally to Portsea beach any time soon. But I hope it will someday.